The present invention relates to a system for detecting working limit of electrode tips of a spot welder.
Since the electrode tip of the spot welder wears to be deformed as it is used, the electrode must be periodically reformed into a desired shape by grinding. When a dimension of the electrode reaches a predetermined limit value, the electrode is replaced with a new electrode.
However, since the dimension of the electrode is visually checked by an operator, the electrode may be used over the working limit. As a result, problems such as defective welding arise.
In order to resolve the problem, it has been proposed to provide a warning apparatus for producing a command signal to change the electrode or to stop welding operation when the number of the spot welding stroke reaches a predetermined number.
However, in such a system, a dotting (spotting procedure) without electricity and a test dotting are counted as the number of spot welding stroke. Consequently, the command for changing the electrode tip or stopping the welding operation is produced at a time earlier than a proper changing time, which means a waste of the electrode.
FIG. 4 shows another conventional device for detecting the working limit of the electrode tip disclosed in Japanese Utility Model Application Laid-Open No. 61-107482. The device has a socket 11 in which a used electrode tip 12 to be detected is inserted, a stopper 13 provided on the end of the socket 11 for stopping the inserted electrode tip 12, a detecting rod 14 slidably mounted in the wall of the socket 11 and laterally projected to the inside of the socket, and position detecting means 15 arranged to be operated by the detecting rod 14.
When the electrode tip 12 is inserted into the socket 11 and touched to the stopper 13, the detecting rod 14 is moved by the electrode tip 12. A moving distance of the detecting rod 14 is dependent on a deformed shape of the electrode tip. The position detecting means 15 produces a signal in accordance with the moving distance. Thus, working limit of the electrode tip 12 is determined.
However, such a device is complicated in construction and hence manufacturing cost increases. Further, the device has no possibility to perform the detection automatically during the welding operation.